The present invention relates to an image scanning mechanism used in an image reading apparatus, and in particular relates to one for reading an original image realized on a sheet either by sensing light reflected by the sheet (image reading in such a manner will be referred to as reflection reading hereinafter) or sensing light transmitted by the sheet (image reading in such a manner will be referred to as transmission reading hereinafter). In the transmission reading, the sheet to be used comprises, for example, a transparency.
One example of an arrangement of such an image scanning mechanism will be described with reference to FIG. 1. Such a construction was proposed by the applicant the same as that of the present application, in Japanese Patent Application No. 4-33616 filed on Feb. 20, 1992, inventors of which are Toshiyuki Ando, Osamu Takase, Takahiro Asai, Makoto Hino and Yutaka Kaneko.
FIG. 1 shows an internal arrangement of an image reading apparatus using the above image scanning mechanism. (The shown arrangement is in accordance with that proposed by an application filed by the present applicant.) A contact glass 1, acting as a sheet table, is used for placing thereon a sheet 2, for reflection reading (such a sheet will be referred to as a reflecting sheet, hereinafter), on which an original image to be read is realized. Below the contact glass 1 is arranged, a light source 3 for illuminating the sheet 2, and reflecting mirrors 4, 5 and 6 constituting a reflection reading optical system. The light source 3 and the reflecting mirror 4 are mounted on a first carrier 7 and the mirror 5 and 6 are mounted on a second carrier 8. The following components are arranged along the path of light reflected by the reflecting mirror 6: an image-formation lens 9 for reflection reading; a light direction changing mirror 10 having a reflecting surface pivotably supported on a supporting point P; and a photosensitive element 11 (comprising a charge-coupled-device sensor, for example). The above-mentioned components constitute reflection-reading optical system A in the apparatus body 12 of this image reading apparatus.
A transmission-reading optical system B is provided on the left side of the apparatus body 12 as shown in FIG. 1 and described below. A contact glass 13, acting as a sheet table, is used for placing thereon a sheet 14, for transmission reading (such a sheet will be referred to as transmitting sheet, hereinafter), on which an original image to be read is realized. The contact glass 13 is linked to a second carrier 8. Above the contact glass 13, a light source 15 for illuminating the transmitting sheet 14, and a reflecting plate 16 and a diffusing plate 17 for guiding light onto the surface of the transmitting sheet 14 are arranged. Below the contact glass 13, a reflecting mirror 18 is provided. Along the path of light reflected by the reflecting mirror 18, an image-formation lens 19 for transmission reading and a reflecting mirror 20 are arranged. The light direction changing mirror 10 is oriented as indicated by the symbol R when the transmitting sheet 14 is read and is oriented as indicated by the symbol Q in FIG. 1 when the reflecting sheet 2 is read.
An operation of reading the reflecting sheet 2 in the arrangement shown in FIG. 1 will now be described. The first carrier 7 carrying the light source 3 and the reflecting mirror 4 and the second carrier 8 carrying the reflecting mirrors 5 and 6 are moved along the direction X (sub-scanning direction) shown in FIG. 1, the ratio of moving speeds between the first and second carrier 7 and 8 being 2:1. Thus, the entire original image realized on the reflecting sheet 2 is progressively read. The light reflected by the reflecting sheet 2, associated with the original image to be read, is then reflected by the reflecting mirrors 4, 5 and 6 successively. Then, after that, by means of the image-formation lens 9, the resulting light is used to form the relevant image on the photosensitive element 11, the formed image being then detected by the photosensitive element 11. The photosensitive element 11 outputs a signal corresponding to the detected image, the output signal being then processed by an image processing unit in the apparatus body 12 and not shown in FIG. 1.
Subsequently, an operation for reading the transmitting sheet 14 in the arrangement shown in FIG. 1 will now be described. The light emitted by the light source 15 is reflected by the reflecting plate 16 and diffused by the diffusing plate 17. Then, as a result, the resulting light uniformly illuminates an area, of the contact glass 13, corresponding to the position of the components 15, 18 and 17. Under the condition where the light illuminates the area of the contact glass 13 as mentioned above, the contact glass 13 is moved as a result of being driven together with the second carrier 8 along the direction X (sub-scanning direction) shown in FIG. 1 together with the transmitting sheet 14 placed thereon. Thus, the entire original image realized on the transmission sheet 14 is progressively read. The light transmitted by the transmitting sheet 14 is then reflected by the reflecting mirror 18 and then focused by the image-formation lens 19 so as to form the relevant image on the photosensitive element 11. Before the relevant image is formed on the photosensitive element 11, the light passing through the lens 19 is successively reflected by the reflecting mirror 20 and the light-direction change mirror 10. Then, after that, the photosensitive element 11 outputs a signal corresponding to the detected image, the output signal being then processed by the above-mentioned image processing unit in the apparatus body 12.
In the above arrangement, the sheet table (contact glass 13) used for reading the transmitting sheet 14, such as a transparency is linked to the second carrier 8 for reading the reflecting sheet 2 as mentioned above so that both the sheet table for the transmission reading and the second carrier 8 involved in the reflection reading can be commonly driven. It is also possible to link the sheet table for the transmission reading to the first carrier involved in the reflection reading. That is, a common sub-directional driving system can be utilized as both that of the reflection reading system and that of the transmission reading system. As a result, it is possible to miniaturize and reduce the cost of the image reading apparatus.
One example of an apparatus in the prior art used for the same purpose will now be described. This apparatus is an image reading apparatus disclosed in Japanese Laid-Open Patent Application No. 3-46864. This apparatus reads an original image realized on a sheet placed on a sheet table thereof, the reading being performed by scanning of the image by means of a reading optical system. The apparatus has the capability of reading an image realized on a transmitting sheet film after magnifying it by means of the following arrangement: An image-formation lens for the transmission reading and a device for illuminating the transmitting sheet from a position that is opposite with respect to the sheet to the position where the image sensor is located are attachable; and the image-formation lens is movable in the reading optical system. By this arrangement, it is possible to select a desired mode between two modes comprising a reflection reading mode and a transmission reading mode. Further, it is also possible to read an image realized on a transmitting sheet after magnifying it so as to read the image more accurately.
Another example of an apparatus in the prior art used for the same purpose will now be described. This apparatus is an image reading apparatus disclosed in Japanese Laid-Open Patent Application No. 3-55961. This apparatus reads an original image realized on a sheet placed on a sheet table thereof, the reading being performed by scanning of the image by means of a reading optical system. An image realized on a transmitting sheet such as a film is read by the following arrangement: A sheet table may be located so as to block a light path extending between a light source and an image-formation lens. By such an arrangement, it is possible to select the reflection reading and transmission reading modes as desired. Further, it is also possible to shorten the distance between the transmitting sheet and the image-formation lens in the transmission reading mode. As a result, an image can be read at high magnification and thus with high accuracy in the same mode.
Another example of an apparatus used for the same purpose will now be described. Such an apparatus is a carrier driving unit proposed by the applicant same as that of the present application, in Japanese Patent Application No. 4-182491 filed Jul. 9, 1992, inventors of which are Masanori Saito, Toyokazu Satomi and Toshiyuki Ando. This unit is used for an image scanner which reads an original image realized on a sheet placed on a reflecting sheet table thereof, the reading being performed by scanning of the image by means of a reading optical system. In the scanning, first and second carriers such as mentioned above are driven, the ratio of moving speeds between the first and second carriers being 2:1. A steel belt instead of the commonly used wire is used for driving one of the first and second carriers as described below. Further, a linear motor is used for driving the other one of the first and second carriers.
Respective FIGS. 2A and 2B show side elevation views of the above-mentioned second carriers, used in the above proposed carrier driving unit not shown in FIGS. 2A and 2B. As shown in FIGS. 2A and 2B, shifting pulleys 43a and 43b are rotatably supported on the side of the second carrier, the distance between the pulleys 43a and 43b being relatively small. Turning pulleys 44a and 44b are rotatably supported on an apparatus body 12 not shown in FIGS. 2A and 2B, the distance between the pulleys 44a and 44b being fixed. The steel belt 45 is wound on the shifting pulleys 43a and 43b so that a semicircle on each pulley is in contact with the belt 45. Further, the steel belt 45 is wound on the turning pulleys 44a and 44b so that a semicircle on each pulley is in contact with the belt 45. As shown in FIGS. 2A and 2B, both-direction portions of the belt 45 are first wound on the turning pulleys 44a and 44b so that both-direction portions of the belt extend in inward-pointing directions. Further, both-direction portions of the belt 45 extending after being wound on the respective turning pulleys 44a and 44b are then wound on the respective shifting pulleys 43a and 43b so that both-direction portions of the belt extend once again in outward-pointing directions. Further, both ends 48 of the belt 45 after being wound on the respective shifting pulleys 43a and 43b are then fixed on the apparatus body 12. The above-mentioned first carrier not shown in FIGS. 2A and 2B is clamped on the belt 45 at the clamping part 47.
FIG. 2A shows a state in which the shifting pulleys 43a and 43b linked to the second carrier are at a reading scanning start position. FIG. 2B shows a state in which the shifting pulleys 43a and 43b linked to the second carrier are at a reading scanning end position as a result of the scanning operation being executed through the shifting of shifting pulleys 43a and 43b from the reading scanning start position. By the above-mentioned arrangement, it is possible to improve the accuracy, with which the image is read with respect to the sub-scanning direction.
Generally speaking, there is a demand to read an original image realized on a transmitting sheet with a higher accuracy than in the case where an original image realized on a reflecting sheet is read. In order to fulfill such a demand in an apparatus in which both the reflection reading and the transmission reading may be performed, the following operation is required: Accuracy should be higher in the transmission reading than the reflection reading case, with which accuracy a carrier is driven in the sub-scanning direction so as to scan and thus read the image. However, such a function as making the sub-scanning driving accuracy higher is not described in any of the following three applications mentioned above: the application proposing the arrangement as shown in FIG. 1; Japanese Laid-Open Patent Application No. 3-46864; and Japanese Laid-Open Patent Application No. 3-55961.
The object of Japanese Patent Application No. 4-182491 mentioned above is to make the sub-scanning driving accuracy higher. However, the relevant arrangement shown in FIGS. 2A and 2B may create the following problems: The relevant assembling work may become difficult because the manner in which the belt 45 is wound on the pulleys 43a, 43b, 44a and 44b is complicated as shown in FIG. 2A and 2B. Further, the bending direction of the belt 45 is changed between the position at which the belt is wound on the shifting pulley 43a or 43b and the position at which the belt is wound on the turning pulley 44a or 44b. As a result of such a bending direction change, the driving of the carrier may not be executed smoothly. Further, in the arrangement of the proposed carrier driving unit, another belt is provided on the side of the carrier opposite to the side shown in FIGS. 2A and 2B. The belt length and the manner in which the belt is wound are different between both belts so that the belt winding manner is more complicated in one belt and belt length is longer in that belt. As a result, it is difficult to make the tension in both belts equal.